Use of composite structures throughout the boat, tonneau cover, and automotive parts industries is known in the art. As is also known in the art, prior art composite structures include those having a first layer, or show surface, commonly referred to as a styrenated unsaturated polyester layer, and a second layer, commonly referred to as a styrenated unsaturated polyester resin backing layer. The backing layer functions to provide support and durability to the complete composite article.
It is also known in the art that, during application of the first and second layers to a mold substrate, large quantities of styrene monomer, which is considered a volatile organic compounds (VOC), are emitted. The emission of VOCs is undesirable for environmental, health, and safety reasons. As a result of the quantities of styrene monomers associated with the composite structures of the prior art, the industry has sought to eliminate certain layers in the composite structures that include styrene.
In response to the need outlined above, the industry is moving toward composite structures that have the same first layer described above but a different second layer. This different second layer is a polyurethane or polyurea backing layer that is the reaction product of an isocyanate component with a resin component. The resin component includes a polyol or polyamine and a catalyst. However, the composite articles of the prior art that already include a polyurethane or polyurea backing layer as the second layer are deficient for various reasons.
Generally, the polyurethane and polyurea backing layers of the prior art, when used in combination with a styrenated unsaturated polyester layer, “set-up” or react too quickly. For instance, when the backing layer, i.e., the polyurethane or polyurea layer, is applied to the first layer, i.e., to the styrenated unsaturated polyester layer, cross-linking is necessary between the polyurethane or polyurea backing layer and the styrenated unsaturated polyester layer for adhering the backing layer to the first layer. The polyurethane and polyurea backing layers do not sufficiently cross-link with the styrenated unsaturated polyester layer when the reaction is too quick. Ultimately, the bond between the polyurethane or polyurea backing layer and the styrenated unsaturated polyester layer is unacceptable because there is insufficient cross-linking between the layers.
In the prior art, the various components of the backing layer have been adjusted to increase the reaction time by adding an imidazole-based catalyst to the resin component. However, the composite structures resulting from the slower reactivity exhibit insufficient resistance to heat distortion for the above mentioned applications.
U.S. Pat. No. 5,482,648 to Borden et al. (the '648 patent) focuses on minimizing blistering in a resultant composite structure, and includes the catalyst system to ensure reaction of all functional components of the isocyanate and polyol components. More specifically, the '648 patent discloses a catalyst system including a first and a second peroxy-based compound for use in production of a polyurethane system. The first peroxy-based compound is active at room temperature and the second peroxy-based compound is active at a temperature of at least 167° F. The second peroxy-based compound is activated by an exothermic reaction resulting from the first peroxy-based compound catalyzing a reaction between isocyanate and polyol components. However, the isocyanate-reactive components and catalysts are not optimized to achieve sufficient cross-linking density necessary to result in resistance to heat distortion, as indicated through heat distortion temperatures, consistent with the subject invention.
The catalyst system of the '648 patent would not work with the composite structure of the subject invention. Peroxy-based compounds do not sufficiently catalyze the reaction between the isocyanate component and the isocyanate-reactive component of the subject invention and are too slow, given the functionality of the isocyanate-reactive component. Furthermore, the composite structures of the '648 patent do not achieve sufficient cross-linking density to be sufficiently resistant to heat distortion.
The polyurethane and polyurea backing layers of the prior art have not, to date, been optimized for use with styrenated unsaturated polyester layers. More specifically, the resin components have not been optimized for the type of the particular isocyanate-reactive components and catalysts in the backing layer to provide sufficient reaction time of the backing layer and to achieve sufficient cross-linking density, and thus resistance to heat distortion.
Due to the deficiencies in the composite structures of the prior art, including those described above, it is desirable to provide a novel composite structure having a styrenated unsaturated polyester layer backed by a polyurethane or polyurea backing layer that reacts to provide sufficient reaction time for allowing the backing layer to sufficiently cross-link with the styrenated unsaturated polyester layer, yet provides sufficient cross-linking density to render the composite structure sufficiently resistant to heat distortion.